1. Field of the Invention
This invention relates to an image processing system, comprising:
a system of n fixed real cameras arranged in such a way that their individual fields of view merge so as to form a single wide-angle field of view for recording a panoramic scene; PA1 an image construction system simulating a mobile virtual camera continuously scanning the panoramic scene to furnish a target sub-image corresponding to an arbitrary section of the wide-angle field of view and constructed from adjacent source images furnished by the n real cameras. PA1 a luminance equalizing system including first and second luminance correction modules (LUT.A, LUT.B), which apply a first and a second correction law (Gi, Gj), respectively, to the first and second sets (R,S) of the corresponding luminance levels of a first and a second portion (Ivi, Ivj) of a digital target image Iv formed from two adjacent digital source images (Ii, Ij), to equalize these corresponding luminance levels, in accordance with the condition Gi(R)=Gj(S). PA1 1) varying the panoramic orientation (PAN), referred to as azimuth angle, of its optical axis, corresponding to a variation in the orientation parallel to a horizontal plane of this optical axis passing through a fixed view point common to both the fixed real camera and the mobile virtual camera; which panoramic variation is seen by the viewer as a control means enabling the mobile camera to be pointed to the fight or to the left; PA1 2) varying the orientation (TILT), referred to as angle of sight, of its optical axis, always passing through the view point, in a vertical plane; a variation seen by the viewer as a control means which he can use to point the camera up or down; PA1 3) varying the focal length of the virtual camera which renders it possible to furnish a more or less enlarged target image; a variation which the viewer sees as a ZOOM effect. PA1 which computes a law F establishing a correspondence between the levels of the first set (R) of luminance levels of the first portion of the target image (Ivi) and the levels of the second set (S) of the luminance levels of the second portion of the target image (Ivj), so that S=F(R) and which thereafter computes the first and second correction laws (Gi, Gj) to be applied in the first and second luminance correction modules (LUT.A, LUT.B) to equalize to the best possible extent the corresponding luminance levels in accordance with the relation (Gi(R)=Gj[F(R)]. PA1 a first memory module (MEM.A) selecting and storing a first sub-set (Ai) of pixels of the first part of the target image (Ivi) comprising a first sub-set (r) of luminance levels; PA1 a second memory module (MEM.B) selecting and storing a second sub-set (Aj) of pixels of the second image portion (Ivj), comprising a second sub-set (s) of luminance levels;
This system is used in monitoring devices and in panoramic sighting devices for mobile engines.
2. Description of the Related Art
An image processing device is known from Patent Application WO 92-14341, corresponding to U.S. Pat. No. 5,187,571. This document describes an image processing system for television. This system comprises a transmitter station including a plurality of fixed cameras arranged adjacent to each other so that their fields of view merge and form a wide-angle field of view. This system also comprises a processing station including means for generating a composite video signal of the overall image corresponding to the wide-angle field of view, and means for selecting a sub-image from this composite image. This system also comprises means such as a monitor for displaying this sub-image. This sub-image corresponds to a field of view having an angle which is smaller than that of the composite image and is referred to as a sub-section of the wide-angle field of view.
This image processing system is only suitable for conventional television systems in which the image is formed line by line by means of a scanning beam.
The processing station enables a user to select the sub-section of the wide-angle field of view. The corresponding sub-image has the same dimension as the image furnished by an individual camera. The user selects this sub-image by varying the starting point of the scan with respect to the composite image corresponding to the wide-angle field of view. The wide-angle field of view has an axis which is parallel to the video scan, with the result that the starting point for the video scan of the sub-image may be displaced arbitrarily and continuously parallel to this axis.
The angle of the field of view to which the sub-image corresponds may be smaller than that of a real camera. However, the localization of the sub-image does not include a displacement perpendicular to the scan; its localization only includes displacements parallel to this scan. The formation of the sub-image does not include the zoom effect with respect to the composite image, i.e. the focal change of the sub-image with respect to the focal length of the image pick-up cameras.
The image processing station thus comprises means for constructing the selected video sub-image line after line. These means essentially include a circuit for controlling the synchronization of the video signals from the different cameras.
The present invention has for its object to solve the problem encountered when the constructed sub-image or target image is a digital image, and is computed from at least two portions of adjacent digital source images each furnished by a real fixed pick-up camera, these two cameras being arranged in such a way that their fields of view merge. In this case, a boundary line appears in the target image between the two adjacent target image portions computed from the two different source images. This is caused by the fact that each one of the two real cameras furnishes a source image which, overall, has a luminance which slightly differs from the luminance of the other source image, and that the resultant target image portions also have slightly different luminances.
This luminance difference between the two target image portions computed from the source images provided by the two adjacent cameras is the reason that the reconstructed target image is not perfect.
This boundary line is located between the picture elements computed from the picture elements of the source image of the first fixed camera, and the picture elements computed from the source image of the second fixed camera.
If the target image is constructed from the picture elements of more than two cameras, there will be as many boundary lines as there are groups of two adjacent cameras.